Electronic structure changes across the charge density wave transitions in LaAgSb2
Ashish Atma Chainani1*, J.H. Li1,2, A. Singh1, Y.F. Liao1, Y.Y. Chu1, K. D. Tsuei1, D. J. Huang1,2, C.N. Kuo3, C. S. Lue3
1Condensed Matter Physics, NSRRC, Hsinchu, Taiwan
2Physics, NTHU, Hsinchu, Taiwan
3Physics, NCKU, Tainan, Taiwan
* Presenter:Ashish Atma Chainani, email:chainani.ash@nsrrc.org.tw
We study the electronic structure of LaAgSb2, using bulk sensitive temperature dependent (20 K – 220 K) Hard X-ray photoemission spectroscopy (HAXPES). LaAgSb2 exhibits two charge-density-wave (CDW) transitions, one below T1 = 207 K with a modulation wave vector (0.026,0,0) along the crystallographic a-axis, followed by a second CDW transition below T2 = 186 K along the c-axis with a modulation vector (0,0,0.16), accompanied with weak kinks in the electrical resistivity [1-3]. Recent studies have identified a Dirac-cone band dispersion in LaAgSb2 and nested Fermi surfaces at a low temperature of T = 16 K, but temperature dependent measurements were not reported[4]. We use a bulk sensitive spectroscopy technique to investigate temperature dependent changes in the electronic states of La, Ag and Sb in order to identify states responsible for the CDW transition in LaAgSb2. Temperature dependent HAXPES core level measurements show that the La 3d and Ag 3d core-levels show negligible changes across the CDW transitions. In contrast, temperature dependent measurements show a clear well-separated satellite of the Sb 3d core levels below T1, and the spectral intensity of the satellite progressively increases on lowering the temperature below T2. The temperature dependence of the Sb 3d satellite feature suggests a second order transition, consistent with the known BCS behavior of temperature dependent superlattice reflections by x-ray diffraction[3]. The valence band spectra also indicate a purely anionic character CDW transition, with no involvement of the La and Ag cationic derived states.

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Keywords: charge density wave, strongly correlated system, hard x-ray photoemission spectroscopy